Isobaric Process
P = const, W = PΔV.
Key Notes
Isobaric process: pressure stays CONSTANT (ΔP = 0).
On PV diagram: HORIZONTAL line.
Work done by gas: W = P·ΔV — simple area calculation.
Heat absorbed: Q = nC_p·ΔT, where C_p = (f/2 + 1)R = molar specific heat at constant P.
Change in internal energy: ΔU = nC_v·ΔT (always, for ideal gas).
Volume and temperature linked: V/T = constant (Charles's law).
Examples: water boiling in an open pot (P_atm constant), gas expansion against atmospheric pressure.
C_p > C_v because some heat goes into expansion work (Mayer's relation: C_p − C_v = R).
Formulas
Equation (Charles's law)
Volume proportional to absolute T.
Work done by gas
Pressure times volume change.
Heat absorbed
C_p for constant pressure.
Internal energy change
Always — depends only on T for ideal gas.
C_p vs C_v
Mayer's relation; extra R goes to expansion work.
Important Points
Isobaric ⇒ ΔP = 0 ⇒ work = PΔV.
On PV diagram: HORIZONTAL line. Area = work.
Q is split between ΔU and W: Q = ΔU + W.
Heating gas at constant P: gas expands → does work → needs more heat for same ΔT (hence C_p > C_v).
Charles's law: V/T = const at constant P.
Cooking in open pot: water at 100°C, atmospheric pressure ⇒ isobaric until water boils away.
Isobaric Process notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 11 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.